1. Field of the Invention
The present invention relates to fiber-forming polyamide compositions useful in the manufacture of strain-resistant textile substrates. More specifically, the polyamide compositions comprise modified nylon 6,6, nylon 6, or nylon 6,6/6 copolymers prepared by salt-blending the precursor salt of such polymers with a cationic dye modifier followed by copolymerization and subsequent melt-blending of the resulting copolymer with about 1-15%, based on final polymer weight, of a polyamide formed from reactants having from 8 to 22 carbon atoms per amide link. The polymer compositions of the current invention are particularly useful in the manufacture of dyed or undyed woven, knitted, or tufted textile materials, and molded nylon or composite products.
2. Prior Art
Polyamide textile materials which resist dyeing by acid dyestuffs are well-known in the art. Polyamide substrates have been rendered stain-resistant by treatment with a dye-resist agent, also referred to herein and in the prior art as a stain-resist agent, such as a sulfonated phenol- or sulfonated naphtol-formaldehyde condensation product. Such dye-resist agents have been applied to the fibers comprising the article as a coating from a spin finish, or the substrate in the form of a yarn or woven, knitted, or tufted fabric has been treated in a process wherein the stain-resist composition is applied via immersion, padding, spraying, or other application means in either a batch or continuous process. Such processes are useful for the production of woven, knitted, or tufted polyamide substrates which resist staining by various acid-dye colorants such as those often present in food-stuffs. Because the aforementioned processes involve treatment of the fiber surface, these materials suffer from the disadvantage that the stain-resistance tends to deteriorate with wear. Such processes also are not effective in the manufacture of cut-pile carpets in which the pile comprises hollow-filament or cellular polyamide yarns, because the surface treatment does not sufficiently protect the interior voids of the filament and tip-staining occurs as the solution is taken up by the filament voids via capillary action.
It is known from Flamand U.S. Pat. No. 3,542,743, Crampsey U.S. Pat. No. 3,640,942, and Ucci U.S. Pat. No. 4,579,762 that polyamide materials may be rendered resistant to staining by acid dyestuffs by copolymerizing the nylon with cationic dye modifiers such as aromatic sulfonates. While the acid-stain resistance of these materials is greatly improved versus unmodified polyamides in products that are dyed to medium and deep shades, lighter shade or undyed products are visibly and permanently stained when left in contact with a solution containing typical acid dyes used as colorants for foodstuffs, e.g. FD&C Red Dye No. 40, for a period of several hours.
Thomm et al., U.S. Pat. No. 3,846,507, disclose fiber-forming polyamides having improved basic dye affinity and reduced acid dye affinity which polyamides contain benzene sulfonate units and which polyamide is blended with a normal polyamide, such as nylon 6.
Japanese Patent Application Publication 1-223908, published Sept. 7, 1989, discloses stain-resistant polyamides based on nylon 6, nylon 6,6, nylon 4, nylon 7, nylon 11, nylon 6, 10, etc., which contain a sulfonate-containing aromatic compound of the general formula ##STR1## where X is any of COOH, RCOOH, COOR', RCOOR', and RNH.sub.2 (R is a C.sub.1-5 alkylene group; R' is a C.sub.1-5 alkyl group;) Z is an aromatic group; m and n are 1 or 2; M is hydrogen, an alkali metal or an ammonium group. Preferably the sulfonate group content is in the range 0.1-5.0 mole % of the polyamide constituting units, with a terminal amino group content being not more than 10 eq./T.